Skin hyper-pigmentation comes from various origins such as the hormonal disorder followed by the inflammatory response of skin, genetic disease and ultraviolet irradiation, mainly the synthetic disorder and distribution disorder of melanin pigment.
The main function of melanin is scavenging oxygen radical, which can protect skin from the injury. Therefore, it has been known that the plenty of melanin shows potent response on skin system for protecting skin from physical or chemical toxic substance. Melanin is formed by serial steps i.e., converting tyrosine to dopaquinone by tyrosinase enzyme followed by further enzymatic reaction and spontaneous oxidative reaction and so on.
Therefore, the inhibiting methods of melanin biosynthesis for protecting skin tanning are classified by follows: (1) UV protecting method to get rid of the main cause of melanin formation, which is expected to give satisfactory results (2) Inhibiting method of core carbohydrate biosynthesis necessary to tyrosinase activity (3) Inhibiting method of the function of tyrosinase enzyme participating in melanin formation using by kojic acid or arbutin (4) Inhibiting method of cell differentiation using by hydroquinone which has specific toxicity on melanocyte, melanin forming cell, (5) Decolorizing method by reducing melanin formation.
Ascorbic acid, a functional substance showing various physiological activities can be easily decomposed because of its unstable structure and has strong reducing effect since it has endiol group, one double bond group attached to two hydroxyl group within the molecule. It is oxidized to dehydroascorbic acid by the action of ascorbate oxidase enzyme in vivo. The reaction is reversible and it plays a role in maintaining the redox system in vivo, the metabolism of tyrosine, phenylalanine etc. The formation of dark-brown colored melanin from tyrosine is inhibited by ascorbic acid. However, since the ascorbic acid has similar structure to gamma-lactone structure, it is unstable to light, air, water and heat and so on therefore it is easily oxidized to dehydroascorbic acid. In the oxidation reaction of ascorbic acid, ascorbic acid is transformed into dehydroascorbate radical, a oxidizing intermediate, by the action of the dissociation of hydrogen ion, i.e., successive two electronic transition processes and two reactive radicals itself react each other resulting in the formation of one molecule of ascorbic acid and dehydroascorbic acid (Williams, N. H. & Yandell, J. K.; Aust. J. Chem., 35(6) pp 1133-44, 1982).
Antioxidants react with the dehydroascorbate radicals to reduce its leaving group and thereby inhibit the oxidative reaction. The oxidative reaction of ascorbic acid is reversible the oxidized form of dehydroascorbic acid shows vitamin like physiological activities. However, the dehydroascorbic acid is easily hydrolyzed into 2,3-diketo-L-gulonic acid and the acid is more easily dissociated than other general carbonic acid due to two keto group neighboring on carboxyl groups, and thus the formation of lactone having low degree of freedom between atoms is difficult because of its rigidity such as bond angle (120°) of keto group. Accordingly, it is irreversibly dissociated into L-lyxosic acid and L-xylosic acid which has no physiological activities as an ascorbic acid (Staudinger, H., Krisch, K.; Ann. N.Y. Acd. Sci., 92, pp 195, 1961).
Ascorbic acid is very soluble in aqueous solution while sparingly soluble in non-aqueous solution, however it is difficult to be used in medicine, food, cosmetics etc because of its instability to oxidation. There have been previous reports on the synthetic or enzymatic methods to produce modified ascorbate derivatives such as ascorbate sulfate salt, ascorbate phosphate salt, alpha-glycosyl-L-ascorbic acid and so on:
For example, Japanese Patent Publication No. 5,920/83 filed with the inventor's name of Ishio et al and Japanese Patent Publication No. 198,498/83 filed with the inventor's name of Masamoto et al disclose several synthetic methods for preparing alpha-glycosyl-L-ascorbic acid, however the methods have several disadvantages such as low yield, complex mechanism, the difficulty in obtaining the in-toxicity and safety of final products. Accordingly, there have investigated to develop enzymatic method for preparing the glycoside form thereof (glycon type) till now by specific enzyme such as cyclodextrin glucano-transferase and alpha-glucosidase enzyme.
alpha-glucosidase enzyme has been reported to hydrolyze alpha-1,4-linked alpha-glucose units located in terminal ends of dextrin and to have dual functions such as synthesis and hydrolysis of alpha-glycosyl-L-ascorbic acid according to the reaction condition. It has been reported that 2-O— alpha-D-glucopyranosyl-L-ascorbic acid, a glucosylated ascorbic acid, is prepared by using alpha-glucosidase enzyme isolated from mouse intestine (Noris M. et al., Agricultural and Biological Chemistry, 54, pp 1697-1733, 1990) and mixed enzyme, i.e., cyclodextrin glucano-transferase and alpha-glucosidase enzyme (Japanese Patent Nos. 2926412 and 2832848; Korean Patent Registration Nos. 158102 and 162495).
Korean Patent registration No. 207958 invented by the present inventors discloses a method for producing alkyl fructoside using levan sucrase, a sort of fructotransferase enzyme. International Patent Publication No. WO 01/29185 (A1) invented by the present inventors discloses the purification of novel fructotransferase gene from a microbe and the method for producing di-D-fructofuranose-2,6′:6,2′dianhydride by transferase activity thereof.
However, there have been no disclosure or suggestion on the novel cosmetic use of beta-fructosyl-L-ascorbic acid derivatives showing improved stability to oxidation and the preparation thereof in above disclosed prior references.
Therefore, the present inventors have endeavored to find chemically stable substance using ascorbic acid as a fructosyl group receptor.
Finally, the present inventors have found that chemically stable beta-fructosyl-L-ascorbic acid derivatives prepared by the method of the present invention have potent inhibiting activity of tyrosinase activity.